The present invention relates to a vehicle seat reclining device for adjustably fixing an angle of a seat back relative to a seat cushion, and more particularly to a vehicle seat reclining device, which is adaptable to a case that a large load is applied to a seat back.
As a vehicle seat reclining device, there is known a device, which is constituted by a body frame installed at a base plate of a seat cushion and a cover member installed at an arm plate of a seat back, and which is arranged to limit a relative rotation between the body frame and the cover member and to maintain an angular position of the seat back by engaging an external gear of a lock tooth attached to the seat back with an internal gear formed on an inner peripheral surface of the cover member.
In order to fix the lock tooth, a shaft portion and a pair of guide portions are formed in the vicinity of the body frame, and the lock tooth has a depressed bearing portion, which is swingably connected to the shaft portion and a sliding surface, which slides in contact with the guide surfaces of the pair of guide portions and is coaxial with the bearing surface. A cam for pushing the lock tooth to the outer side so as to engage the external gear with the internal gear is provided at a center portion of the internal gear.
In the thus arranged conventional vehicle seat reclining device, the lock tooth receives an external force of rotating the seat back in the reclining direction generated during a vehicle collision, through the engagement between an internal gear and an external gear. At this moment, since the lock tooth is supported by the shaft portion and one of the pair of the guide portions, the rotation of the cover member relative to the body frame is limited, and therefore the seat back is not rotated from a predetermined angular position.
Although a belt anchor for supporting a force applied to a seat belt is conventionally provided at a center pillar of a vehicle body, there has been lately increased a type that the belt anchor is provided at a seat back. Therefore, in case of the belt anchor provided at the seat back, an inertia force due to a weight of a vehicle occupant during a vehicle collision is transmitted to the seat back through the seat belt, and therefore a force greater than that of a type that the belt anchor is provided at the center pillar is applied to the seat back in the forward direction. Accordingly, the vehicle seat reclining device of the type that the belt anchor is provided at the seat back is requested to be durable to a further large load.
Japanese Published Patent Application No. 2004-121508 discloses a typical vehicle seat reclining device. This conventional vehicle seat reclining device is arranged to form a clearance between one of a pair of guide portions 112A and 112B and an external gear side of a lock tooth 110 so that when a rearward directional load is applied to the seat back and a load is applied from the cover member to the lock tooth 110 through an external gear 110d and an internal gear 107a, a force of rotating the lock tooth at the present position so that the lock tooth 110 enters the clearance. As a result, a shaft portion side of the external gear 110d is pushed toward the internal gear 107a, and the engagement strength between the external gear 110d and the internal gear 107a is increased.